Add URL parsing tests from WHATWG

[tomchristie]

Add 563 URL parsing test cases from https://url.spec.whatwg.org/

Test cases are from...

• https://github.com/web-platform-tests/wpt/blob/master/url/resources/urltestdata.json
• We're only testing the non-failure cases here.

TODO:

• We've got a private import here, which we're avoiding in all our other tests case.
• Add username/password checks.
• We've two failing cases here.

Reminder to self follow-ups:

• Comparison of WHATWG percent-escape set vs. chrome percent-escape set.
• Exceptions for invalid domain names. ^*

^{* eg. see this comment for useful context}

[tomchristie]

Not complete, but suitable for preliminary review.